I downloaded the latest bios A--08 executable file for update the bios but the file is not opening. And the prompt is also not coming for yes or no. It is loading but not starting...

I want to upgrade my Intel Pentium G630 processor to I5 3470 processor.

And does A-08 bios version support third generation processor??

Have you tried the alternate installation under DOS?

This forum post and this one list the Gen 2 as the highest CPU you can install. And the A10 BIOS was released in 2013, the newest is A08 released in 2020.

However Hardware Corner here states that the 3rd Gen CPU is compatible. So a maybe but using A08 BIOS version.

Let me try updating the bios to A08 

I tried it but it is showing OpenSFX Err: Signature SFX mismatched

no evidence on user benchmark that 620 supports i5-3470. 
otoh Inspiron 660 definitely supports i5-3470.

It says “The motherboard is using the H61 chipset and supports 3th gen Intel Core processor”.  but it provides no link or evidence to validate the claim.

H61 is a sandy bridge chipset which natively supports Intel 2nd gen cpu only.  To support 3rd gen it requires a vendor bios update.  “Sandy Bridge chipsets, except B65, Q65 and Q67, support both Sandy Bridge and Ivy Bridge CPUs through a BIOS upgrade”

so the question is, did Dell release a bios update for 620 to support Ivy bridge cpu aka Intel 3rd gen?  There are only two versions of bios on Dell site, neither mentions anything on microcode update.

otoh, this community reports “Dell Inspiron 620 can not handle Ivy Bridge CPUs like the i5-3000 series.  Someone who also had a Dell Inspiron 620 mentioned in this old Tomshardware.com forum page attempted to install an i5-3570k processor and the Inspiron 620 computer would not boot up at all.”

Here is written that it support 3gen processor

https://www.hardware-corner.net/desktop-models/Dell-Inspiron-620s/

I also login as administrator but the bios executable file not opening. MS-A08 file.

Why it is happening?

I highly doubt switching from bios A10 to A08 is going to make pc post on i5-3470.

the more hurdle you face trying to flash bios, the better you stop fighting it as it increases risk of failed flash and bricking mobo. If pc boots well intel 2nd gen cpu now, it is working. No need to update bios.